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Bureau of Mines Information Circular/1986 



Development of Protective Operator 
Compartment for Thin-Seam Mobile 
Bridge Carrier , 

By A. J. Kwitowski and Robert J. Gunderman 




UNITED STATES DEPARTMENT OF THE INTERIOR 



Information Circular 9093 



Development of Protective Operator 
Compartment for Thin-Seam l\/lobile 
Bridge Carrier 

By A. J. Kwitowsl(i and Robert J. Gunderman 




UNITED STATES DEPARTMENT OF THE INTERIOR 
Donald Paul Model, Secretary 



BUREAU OF MINES 
Robert C. Morton, Director 




r)0> 9 Oil 



Library of Congress Cataloging-in-Publication Data 



Kwitowski, August J. 

Development of protective operator compartment for thin-seam 
mobile bridge carrier. 



(Information circular; 9093) 
Supt. of Docs, no.: I 28.27: 9093 



1. Coal-mining machinery. I. Gunderman, Robert J. II. Title. III. Series: Information 
circular (United States. Bureau of MinesI; 9093 



TN295.U4 [TN813] 622 s (622'.3341 86-600036 



CONTENTS 

Page Page 

Abstract 1 Preliminary design and analysis ^. 8 

Introduction 2 Compartment design 9 

Description of double bridge carrier 2 Seat and controls 11 

Conceptual development of the operator Mockup evaluation 12 

compartment 4 Detailed design of the operator compartment .... 16 

Operator functions observed underground 4 Evaluation prior to shipment 20 

Mine applications 5 Underground evaluation 25 

Operator compartment requirements and impact 5 Summary 27 

Operator position 5 

Operator location 6 

Impact on machine and application 8 



ILLUSTRATIONS 

1. View of double bridge carrier 3 

2. Position of bridge carrier during face change 3 

3. View of Jeffrey model 506C-5 bridge carrier 3 

4. Model 506C-5 controls 3 

5. Potential compartment locations not requiring significant modifications 6 

6. Typical section dimensions used for continuous haulage systems 6 

7. Concept using swing-type conveyors 7 

8. Recommended bridge carrier concept 7 

9. Concept with modified operator placement 7 

10. Plan view of recommended bridge carrier concept 8 

11. Attachment design employing a pivot and sliding entrapment 9 

12. View of compartment attachment used in final design. 9 

13. View of compartment shape 10 

14. Side view of bridge carrier with compartment in place 10 

15. Compartment concept using split canopies 10 

16. Side view of head support concept 11 

17. View of concept for operator controls 11 

18. Detailed view of control rods 12 

19. View of full-scale mockup 12 

20. Operators view toward simulated dolly 12 

21. View of operator looking outby 13 

22. Second view of operator looking outby 13 

23. Reference points used in visibility evaluation 13 

24. View of mockup compartment with 50th percentile operator under a 30-in canopy 14 

25. View across dolly toward a 5th percentile operator under a 32-in canopy 15 

26. View of mockup compartment with 50th percentile operator under a 36-in canopy 15 

27. View of mockup compartment with 95th percentile operator and 32-in canopy 16 

28. Second view of mockup compartment with 95th percentile operator and 32-in canopy 16 

29. View of compartment on right side of bridge carrier 17 

30. Close-up of compartment attachment hardware 17 

31. View of compartment with rear tilted up 18 

32. View of compartment with slides up and rear tilted down 18 

33. View with compartment level and at top of slides 18 

34. View of seat adjustment holes 19 

35. View of canopy hydraulic lift cylinders 19 

36. View of support post raise cylinder, flow-direction valve, and hydraulic pump 19 

37. View of visibility limits with canopy set at 30 in 20 

38. View of visibility limits with canopy set at 35 in 20 

39. View of visibility limits with canopy set at 40 in 20 

40. View of operator position to see in general outby direction 20 

41. View into operator compartment with canopy set at 35 in 21 

42. View of 5th percentile operator with canopy set at 35 in 22 

43. View of 50th percentile operator with canopy set at 35 in 22 

44. View of 95th percentile operator with canopy set at 35 in 22 

45. View of leg position for 50th percentile operator 22 



ILLUSTRATIONS— Continued 

Page 

46. View of leg position for 95th percentile operator 23 

47. View of 95th percentile operator with canopy set at 40 in 23 

48. View of lever controls located in console 23 

49. View of operator activating both tram controls 23 

50. View of operator working discharge conveyor raise-lower and tram controls 24 

51. Detailed view of electrical controls 24 

52. View of operator reach required to start pump motors 24 

53. View of operator reach required to use leftmost pump control 24 

54. View of operator working both electrical and hydraulic controls 25 

55. View of 95th percentile operator working hydraulic controls while looking outby 25 

56. View of rear of operator compartment showing dished sides 26 

57. View of roof clearance with canopy set at 37.5 in 26 

58. View into the operator compartment 26 

59. View of conveyor when raised close to roof 26 

60. View of operator working within compartment 27 

61. View of second operator working within compartment 27 

TABLES 

1. Seam heights of mines using the model 506C-5 bridge carrier 5 

2. Criteria and weight factors for ranking potential compartment locations 7 

3. Mockup evaluation results with different sized operators 13 

4. Summary of collected visibility data 21 



UNIT OF MEASURE ABBREVIATIONS USED IN THIS REPORT 


ft 


foot 


in/ft 


inch per foot 


h 


hour 


mm 


minute 


in 


inch 


st/min 


short ton per minute 



DEVELOPMENT OF A PROTECTIVE OPERATOR COMPARTMENT 
FOR A THIN-SEAM MOBILE BRIDGE CARRIER 



By August J. Kwitowskr and Robert J. Gunderman' 



ABSTRACT 

This Bureau of Mines report summarizes the development of a protective operator 
compartment for a new generation thin-seam mobile bridge carrier. The developed 
compartment is commercially available and is currently employed on approximately 
15 bridge carriers used in the mining industry. The design of the compartment, which 
employed human factors engineering and small- and full-scale mockup models, is fully 
described. Details of the compartment's fabrication, evaluation, and demonstration in 
a commercial low-seam coal mine are also provided. 

'Civil engineer, Pittsburgh Research Center, Bureau of Mines, Pittsburgh, PA. 
Conner project manager, Jeffrey. Mining Machinery Division, Columbus, OH. 



INTRODUCTION 



Since January 1, 1974, Federal law has required cabs 
and canopies on underground face equipment, and this 
has successfully reduced the seriousness of injuries 
sustained on face equipment operators during ground fall 
accidents. The Labor Department's Mine Safety and 
Health Administration (MSHA) has estimated that 
between January 1974 and January 1982, cabs and 
canopies saved 200 lives from roof fall fatalities.^ 

MSHA also estimated that approximately 70% of the 
total 2,212 fatal and nonfatal equipment accidents 
occurring in seams below 48 in during the above period 
could have been prevented if protective structures had 
been employed on all face equipment. 

The coal mining industry's successful use of protec- 
tive cabs and canopies has occurred almost exclusively in 
mines where the floor-to-roof height is 48 in or greater. 
Industry problems with attempts to employ protective 
operator structures in thinner seams were so severe that 
on July 1, 1977, MSHA rescinded requirements for 
operator protective structures on face equipment operat- 
ing in coal seams with a working height of 42 in or less. 

Additionally, many coal operators have been success- 
ful in obtaining variances relieving legal requirements for 
cabs and canopies on machines working in heights above 
42 in. Variances are granted primarily because operators 
have proven under some circumstances that the addition 
of a cab or canopy to a particular machine constitutes a 
safety hazard. 

The pricipal argument used in obtaining variances is 
that cabs and canopies can so impair the operator's field of 



view and comfort that machine control becomes difficult 
and hazardous. The addition of a cab or canopy to a 
machine that operates in low-coal can block the visual 
cues that an operator needs for safe performance through 
the mining cycle. If operators cannot properly perceive the 
position of their machines relative to their surroundings 
and other workers, the safety aspects of cabs and canopies 
can be negated to the point where safety is improved by 
removing the structures. 

This Bureau of Mines project originated with the 
objective of developing and demonstrating a protective 
operator compartment for a low-seam double bridge 
carrier — a primary component of continuous face haulage 
systems. The end product was to be usable in seams below 
48 in. The contractor, Jeffrey Minning Machinery 
Division of Dresser Industries, Inc.,^ selected a goal of 34 
in as the minimum operating seam height. This was based 
on development of a canopy for use on Jeffrey's model 
506C-5 bridge carrier, a primary machine used in seam 
heights as low as 28 in. 

The final product was not a protected operator 
compartment that could be installed on the model 506C-5 
bridge carrier on a retrofit basis; instead, it was designed 
for inclusion on a new mobile bridge carrier, the Jeffrey 
model 5010. The initial phases of the reported work 
assumed that the compartment would be used with the 
model 506C-5 bridge carrier. The decision to switch to the 
model 5010 bridge carrier occurred just prior to the 
detailed design phase. 



DESCRIPTION OF DOUBLE BRIDGE CARRIER 



The double bridge carrier is a unit of continuous 
haulage systems which convey coal from the continuous 
mining machine to the room conveyor. The machine is 
self-propelled, crawler mounted, and manually operated. 
Figure 1 shows a double bridge carrier linking two bridge 
conveyors between the continuous miner and the room 
conveyor. The reach of this system is sufficient for a 
three-entry section. If necessary, a second double bridge 
carrier and another bridge conveyor can be linked into the 
system to provide enough reach for a five-entry section. 
The double bridge carrier operator(s) must maneuver the 
machine(s) to snake the conveyors through the cuts and 
entries. When repositioning the miner during a face 
change, the entire system must be backed up parallel to 
the room conveyor. (See figure 2.) 

Figure 3 shows the Jeffrey model 506C-5 bridge 
carrier in operation; it is intended for use with thin-seam 
continuous mining machines and is less than 25-in high. 



^Sawyer, S. G., and J. A. McCormick. Cabs and Canopies Underground 
Do Protect Miners. Coal Min, and Proc, v. 10, No. 2, 1975, pp. 40-44. 

Zona, A. (Mine Safety and Health Administration, Pittsburgh, PA). 
Private communicatiion, Jan. 1982; available from A. J. Kwitowski, 
BuMines, Pittsburgh, PA. 



The operator controls are located on the left inby side, just 
above the crawler treads. 

The inby bridge conveyor is supported by a carriage 
(or dolly) riding on the receiving conveyor of the double 
bridge carrier. The bridge carrier operator is responsible 
for positioning the machine to allow continuous miner 
movement in either direction. The dolly is free to move 
approximately GVa ft along the conveyor, allowing for 
small movements of the continuous miner without having 
to reposition the bridge carrier. 

The model 506C-5 operator controls are pictured in 
figure 4. The most frequently used controls, the hydraulic 
actuators, are shown on the right side of the figure. The 
control functions are, from left to right: the receiving 
section raise-lower; the discharge section raise-lower; the 
left-hand tram; and the right-hand tram. The electrical 
controls shown in the figure are of the push-type and 
include power on, power off, conveyor forward, conveyor 
off, jog, jog-reverse, automatic, and manual. The system 
also provides an emergency stop bar. 



^The work was done under Bureau contract H0387027; this publication 
was prepared jointly by the contractor and the Bureau in lieu of a 
contractor final report. 




'.:'l 




FIGURE 1-. — View of double bridge carrier. 



FIGURE 2. — Position of bridge carrier during face change. 




FIGURE 3.— View of Jeffrey model 50SC-5 bridge carrier. 



1 

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FIGURE 4.— Model 506C-5 controls. 



CONCEPTUAL DEVELOPMENT OF THE OPERATOR COMPARTMENT 



Jeffrey's approach to the conceptual development of 
the operator compartment included mine visits, consulta- 
tions on human factors, widely varied idea generation, 
and evaluation using small and full-scale mockup 
fabrications. 

The 506C-5 machine was not originally designed to 
allow for the inclusion of an operator compartment and/or 
canopy. It seemed doubtful that a satisfactory compart- 
ment could be designed to employ the controls at their 
standard location at the left inby side of the bridge carrier. 
The first step in the compartment development was to 
schedule mine visits allowing first-hand observation of the 
operator-machine interaction. The idea was to improve 
the odds that the design would contain the full inclusion of 
various operational modes and styles. Considerations of 
human factors were used to formulate a list of questions 
and items to observe while in the mines. 



OPERATOR FUNCTIONS OBSERVED 
UNDERGROUND 

Visits were made to three operating underground coal 
mines to help the designers understand what the operator 
of a double bridge carrier does during a shift. This 
information was essential to the compartment develop- 
ment in indicating correct operator placement, sufficient 
mobility of the machine, and ability of the operator to 
perform all necessary functions from the operating 
location. 

The working heights in the visited mines were 29, 32, 
and 46 to 51 in. A five entry system with two double bridge 
carriers was used in the 32-in mine. The other two mines 
used one double bridge carrier. Roof conditions were 
extremely good in the 29- and 32-in mines. 

Detailed notes were kept for each mine visit. The 
significant items are discussed in the following para- 
graphs. Prior to the visits, a human factors consultant 
helped prepare two lists of things to look for and questions 
to ask. 

The general category list included: 

1. Mine conditions. 

2. Gloves. 

3. Mining plan. 

4. Operations observed. 

5. Modifications to machinery by mine operator. 

6. Cycle times. 

7. Delays and causes. 

8. Records of accidents or near accidents. 

9. Suggestions for improving controls. 

The observations of the operator list included: 

1. Operator position. 

2. Operator size. 

3. Method of communication. 

4. Pattern of head and eye positions. 

5. Present field of view conditions. 

6. Critical field of view areas. 

7. Average time at controls. 

8. Task breakdown (safety, skill, and time). 

9. Order and frequency of control usage. 



10. Operator movement. 

11. Position changes to relieve fatigue. 

12. Ease of learning to operate. 

13. Basis for recognizing good operation. 

14. Causes of poor operation. 

15. Difficulties in reversing. 

16. Operational problems related to control applica- 

tion. 

17. Apparent hazards. 

18. Operator's mistakes in control use and how this 

factor affects safety and production. 

When running coal, the operators stayed close to the 
machine controls. When events were occurring at a 
relatively rapid pace, the operator kept one hand on the 
tram controls. When the pace slowed or was interrupted, 
the operators would often recline against a rib. 

As needed, operators took a shovel from atop the 
machine and cleaned up spillage at transfer points. 
Cleanup was not performed on a fixed schedule, but 
typically was done once per hour. At one installation, the 
routing of cables and water hose coming from the outby 
point toward the continuous mining machine was 
arranged at the coal transfer points so that no manual 
cable and/or hose handling was required. At the other two 
installations, the operator had to leave the controls to 
move the cable and hose when tramming the system. 
Some operators occasionally left their stations to check 
roof conditions. 

The principal operator tasks involved machine posi- 
tioning to keep the dolly centered on the receiving 
conveyor and watching the coal flow for clogs. Occasional- 
ly, the operator had to clear blockage at the transfer 
points. Except during tramming, the receiving section was 
kept lowered to the floor. The discharge section was kept 
high enough to assure that the outby bridge conveyor was 
elevated above the floor and reasonably level. 

Typically, the operator's biggest challenge was tram- 
ming outby. During this activity, the operator had to keep 
one hand on each of the two tram controls, with the 
machine-turning being accomplished by rotating both 
hand-controls. To view clearances, operators needed to 
crawl alongside the machine while it moved outby, 
keeping themselves constantly aware of dolly position, 
ribs clearance for both conveyors and the carrier, and roof 
clearance of both conveyors. If necessary, the operator 
could leave the controls to obtain better visibility. 

Cycle times were recorded at the three mines. The 
percentages of time spent for each function were surpris- 
ingly similar: 70.5% running coal, 9.8% tramming inby, 
16.4% tramming outby, and 3.3% waiting. Thus, operators 
spent approximately 80% of their time facing inby and 
less than 20% facing outby. 

Cap lamp signals provided the main form of com- 
munication between section workers. To use this system, 
the bridge carrier operator needed to be within the 
line-of-sight of the miner operator, the outby helper, tmd 
the second carrier operator (if present). Start-up or 
shutdown of the inby bridge conveyor by the miner 
operator was a signal for the bridge carrier operator to do 
the same with their conveyors. 



MINE APPLICATIONS 

Mobile bridge carriers are used primarily in low 
seams where shuttle-type face haulage vehicles are less 
effective. The model 506C-5 double bridge carrier is used 
predominantly for work behind the Jefiiey model 101 MC 
remote control continuous miner, which works in seam 
heights from 30 to 53 in. Therefore, the model 506C-5 is 
generally found only in lower-height seams. The con- 
veying capacity of the 506C-5 is rated at 6 st/min. 

Sixty-five machine delivery orders were examined to 
assess application requirements and the potential accept- 
ance of a protective canopy over the operator. The seam 
heights at the mine site where the equipment was 
delivered were obtained from Jeffrey's internal data 
and/or coal mine directories (table 1). llie bridge carriers 
may actually have been used at a different mine location 
with a different seam height. 

Table 1. — Seam heights of mines using the model 506C-5 
bridge carrier 



Seam height. 


Number of 


Seam height, 


Numt)er of 


in 


machines 


in 


machines 


28 


2 


39 


6 


29 


3 


40 


2 


30 


2 


42 


5 


32 


6 


43 


9 


34 


3 


45 


1 


36 


10 


46 


6 


38 


8 


48 


2 



According to these data, the mean seam height value 
was 38 in. Ten machines operated in 36-in seams; thus, 
the minimum operating height for the compartment was 
set at 34 in to accommodate 80% of the mine heights in the 
data sample. 

Regardless of its canopy setting, the actual working 
height of a machine is dependent on mine conditions such 
as undulations, high spots, and roof headers. Therefore, a 
machine with a csinopy height set at 34 in cannot operate 
in a working height of 34 in. Provisions have to be made 
for additional lowering of the canopy. 

OPERATOR COMPARTMENT REQUIREMENTS 
AND IMPACT 

After defining operator functions, the important 
questions remaining were location of the operator, 
possible postural positions, and the impact of proposed 
modifications on machine application. Since acceptable 
answers to the first two questions were difficult, they were 
initially considered without any constraints on changes to 
the machine. The following section describes the studies 
and considerations of these questions as related to the 
challenge of providing an operator compartment for a 
34-in working height. 



OPERATOR POSITION 

Operator postural positions are constrained by com- 
partment dimension restrictions. Obviously, an operator 
cannot be seated upright if the canopy height is only 30 in 
above the floor. Also, compartment width must not exceed 



27 in or machine maneuverability will be seriously 
impaired. 

Human factors must be considered in equipment 
design. In a compartment 30-in high and 24- to 27-in wide, 
absolute operator comfort is not possible using established 
principles of design. Compromises must be made on what 
is theoretically desirable and practically possible. Thus, 
the human factors challenge involves how to best meet 
both system design requirements and avoid imdue 
physiological or psychological stress in the operator. 

Key design criteria regarding the operator included: 

1. Maximizing field of view. 

2. Enabling effective use of controls. 

3. Allowing postural change during operation. 

4. Minimizing discomfort and fatigue. 

5. Permitting rapid exit from the compartment. 

6. Protection from roof falls. 

In addition to meeting design criteria, compartment 
space requirements must be held to a minimum to insure 
maneuverability of the bridge carrier. 

Operator comfort is achieved by minimizing static 
work, allowing postural changes, and providing body and 
limb support, especially for the head and neck diuing 
angles of severe back recline. 

Field of view (fore and aft), control activation for 
precise tramming, and bridge height control are impor- 
tant factors affecting operator performance. 

Safety is the keystone criterion in good compartment 
design. A compartment must provide for rapid operator 
egress, prompt emergency stop bar activation, and 
elimination of potential pinch points. The interior 
surfaces of the compartment must protect the operator 
from suffering additional bruises or contusions during 
violent motions, vibrations, roof falls or ribbing collisions. 

A number of candidate operator positions were 
identified emd evaluated jointly by a human factors 
consultant and the Bvireau's contractor. Positions evalu- 
ated included: the prone; on the side with 45° torso 
rotation and elbow support; crouched £md kneeling; 
reclined; half squatting; leaning genuflection; and the dog. 
Posture acceptability varied among tested individuals 
depending on the operator's elasticity, size, personal 
choice, and amount of time spent in a given position. Some 
positions can only be maintained for short time periods, 
while others (like the seat reclining posture with a proper 
back angle) can be maintained for hours. 

The low height requirement (30 in) eliminated some 
postural configurations from further consideration. Posi- 
tions remaining included the prone, side with 45° torso 
rotation and elbow support, and the reclined. These 
configurations all required one dimension of the compart- 
ment in the range of 5 to 7 ft. 

Upon suggestion of the himian factors consultant, 
unobstructive studies of nonmine personnel were con- 
ducted to evaluate tmbiased responses to maintaining 
postures for 1 h within the confines of a compartment 
30-in high, 24-in wide, and 70-in long. Using six college 
students ranging in height from 5 ft 10 in to 6 ft 3 in, a 
series of videotapes was collected while the subjects 
maintained an alert condition in the defined space. Each 
subject was observed for 1 h; 30 min in prone positions 
with buttock either turned to side or top, and 30 min 
reclined on a backrest. The reclined angle of the backrest 



permitted the subjects to sight along the inside top of the 
compartment while still allowing room for a mining 
helmet. This study confirmed anthropometric require- 
ments and indicated more postural changes for nonreclin- 
ing positions. The subjects differed in their personal 
preferences, but the consensus preferred the reclined 
position. Notable leg position changing accompanied the 
reclined position, probably due to the fact that stretching 
the legs in a 60° back angle recline results in stress of the 
hamstring muscles. 

The striking aspect of these tests was the subjects' 
willingness to sit reclined at a 60° back angle for 30-min 
periods. This fact was later verified using test subjects 
within the mockup fabrication. Although subjects above 
the 90th percentile range would have problems with 
muscle discomfort over time, it appears that a compart- 
ment height of 30 in represents the lower limit for reclined 
seating. Below 30 in, either operator size restrictions are 
necessary or an entirely new concept of seating or postural 
placement is required, such as a prone position. 

OPERATOR LOCATION 

Inclusion of an operator compartment approximately 
27-in wide with a 72-in base area was considered for any 
conceivable location on the model 506C-5 bridge carrier. 
The first consideration in determining compartment 
location was maneuverability with no regard for visibil- 
ity, complexity or practicality. 

Figure 5 shows four potential compartment locations 
that would not require significant modification to the 
double bridge carrier. These configurations were graphi- 
cally analyzed to establish maneuver feasibility. 

Entries for continuous haulage systems are typically 
20-ft wide on 50-ft centers. (See figure 6.) Positions 3 and 4 
were eliminated from further consideration because both 
bridge conveyors must be free to swing ± 90° with respect 
to the conveyor on the carrier. 

Potential modifications to the basic model 506C-5 to 
accommodate an operator compartment were considered 
singly and in combination. The potential modifications 
determined were — 

1. Relocating the conveyor outside the crawler drive. 

2. Employing single or double bends in the conveyor 
pan. 

3. Using a swing-type discharge conveyor section. 

4. Using a swing-type receiving conveyor section. 

5. Increasing track width from 1 to 3 ft. 

6. Providing an ingress opening through the center of 
the crawler drive assembly. 

7. Repositioning the operator's leg space under the 
conveyor. 

If significant machine modifications were enacted, an 
additional 13 potential operator compartment locations 
would be possible. These locations were graphically 
analyzed for maneuverability and are listed as follows: 

Position 5. — Between crawler drive assemblies with 
conveyor relocated outside the crawler drive assemblies. 

Position 6. — At 45° to receiving section with 
conveyor relocated outside crawler drive assemblies. 

Position 7. — Parallel to receiving section with 
conveyor relocated outside crawler drive assemblies and 
curved inward 20°. 

Position 8. — Present outboard location with swing 
discharge and double curve receiving conveyor sections. 




KEY 

Nos. |-4 Proposed 

operator com- 
partment locations 



FIGURE 5. — Potential compartment locations not requiring 
significant modifications. 




FIGURE 6. — Typical section dimensions used for continuous 
haulage systems. 



Position 9. — Present outboard location with swing 
discharge section. 

Position 10. — Between conveyor and crawler drive 
assemblies with swing discharge and swing receiving 
sections. 

Position 11. — Crawler drive assemblies moved apart 
1 ft with compartment parallel to swing discharge section. 

Position 12. — Crawler drive assemblies moved apart 
1 ft with compartment parallel to swing discharge section. 

Position 13. — Crawler drive assemblies moved apart 
1 ft with compartment parallel to discharge section. 

Position 14. — Crawler drive assemblies moved apart 
2'/2 ft with compartment between pump motor and 
conveyor. 

Position 15. — Between conveyor and crawler drive 
assemblies with ingress opening through center of a 
crawler drive assembly. 

Position 16. — Operator's legs under the discharge 
conveyor section. 

Position 17. — Operator's legs under the conveyor 
center section. 

Figure 7 shows the concept employing swing-type 
conveyors and figure 8 shows position 13, which was 
ultimately selected for the recommended concept. 




FIGURE 7. — Concept using swing-type conveyors. 




FIGURE 8. — Recommended bridge carrier concept. 




After identification, the various potential compart- 
ment locations were rated by four evaluators using the 
weighted criteria in table 2. Evaluation results showed no 
superior concept and little difference between the highest 
and lowest ranked positions. 

Table 2. — Criteria and weight factors for ranking potential 
compartment locations impact on machine and application 



Criteria 



Weight factors 



Visibility: 

Inby (to tram) 

Receiving transfer 

Discliarge transfer 

Outby (to tram) 

Sides 

Maneuverability 

Communication 

Minimum operating seam height 

Operator protection 

Operator comfort 

Operator emergency exit 

Ingress 

Control accessibility 

Compatibility with personal gear 
Equipment modification 



3.5 

4.25 

3.5 

3.25 

3.25 

4.5 

4.0 

3.25 

4.5 

4.0 

4.0 

2.75 

3.5 

2.25 

3.25 



FIGURE 9. — Concept with modified operator placement. 



A Vs-in/ft-scale cardboard mockup was used for 
additional evaluation; for example, figure 9 (position 17) 
shows an opening between the crawler drive and the 
conveyor where operators with their legs folded beneath 
them would sit facing the conveyor. The model showed 
position 17 provides inadequate clearance and space for 
the operator. 

Practical considerations further reduced the field of 
candidate compartment locations. Swing-type conveyors 
will not work over a range of ±90° without adding 
considerable complexity to the conveyor drive. Any 
increase of more than 1 ft in machine width is 
unacceptable when entry widths are 18 ft or less. These 
considerations narrowed the possible operator locations to 
positions 2, 13, 15, and 16. 

Position 15, one of the more imaginative concepts, 
would have the operator ingress and/or egress through an 
opening in the middle of the crawler drive assembly and 
would locate the treads close to the roof This concept was 
abandoned because it was very inefficient from a space 
utilization viewpoint and locations for machine compo- 
nents could not be readily identified. Also, the operator 
might suffer psychologically from being so enclosed by 
machinery. 

The concept of placing operators facing the conveyor 
was explored since then they could readily see inby or 
outby. This would require the operator's legs to extend 
below the conveyor position. Unfortunately, there was not 
sufficient space available in the vertical direction to 
permit placement of the conveyor and the structure to 
enclose the operator's legs. 

Therefore, position 13 remained the most favorable 
location. (See figure 10.) The compartment is 72 in by 27 
in and is located parallel to the discharge conveyor. 

Although the above concept appeared workable at 
this stage in the compartment development program, it 
would require considerable modification to the basic 
model 506C-5. The hydraulic pump and motor would need 
to be relocated and the crawler drive assemblies would 
have to spread apart by at least an additional foot. These 
problems ultimately led to the recommended compart- 
ment concept being incorporated into the design of a new 
model mobile bridge carrier. 



^^ 




Machine width increased 
approximately 18 in Limited ingress 

or egress — 



FIGURE 10. — Plan view of recommended bridge carrier 
concept. 



All potential locations for a protected operator 
required some increase in machine dimensions, which 
would decrease machine maneuverability. The model 
'506C-5 is relatively maneuverable, allowing the operator 
to easily move out of the way when clearance is minimal. 
However, this maneuverability is achieved at the expence 
of the operator's safety. Therefore, some compromise in 
machine maneuverability must be made to insure 
operator protection. 

There is no engineering guideline concerning growth 
of machine size. Maneuverability analysis of the model 
506C-5 indicated a width change from 7 ft 11 in to 
approximately 9 ft could be tolerable, especially if the 
increased width would be located close to the machine's 
pivot center. If width is increased closer to the conveyor 
ends, maneuverability becomes more difficult. 

Although any length increase would affect turning 
ability, a 1- to 2-ft increase over the model 506C-5's length 
of 22 ft 11 in should havfe no major impact. 

As shown in figure l(j, the machine with the selected 
operator compartment concept is wider than the present 



model. However, refinements to the concept (detailed in 
the following) hold the width increase to approximately 12 
in for the crawler drives and lengthen the conveyor by 
approximately 18 in. 



IMPACT ON MACHINE AND APPLICATION 

The addition of the compartment on the machine 
effected significant changes in addition to length and 
width increases. In order to offset the change in center of 
gravity caused by adding to the length of the discharge 
conveyor, the crawler drive assemblies needed to be 
reversed with as much weight as possible concentrated 
toward the receiving conveyor end. Because the present 
design includes the crawler drive frames and the 
hydraulic tank as an integral part of the mainframe, the 
proposed changes require a totally new mainframe. 
Coupled with the additional costs of a new low-profile 
electrical enclosure and new parts, the required changes 
made a retrofit of existing machines very unattractive. 
However, to use the design concept for the manufacture of 
a new machine would add little cost increase above that 
associated with the addition of a new operator compart- 
ment. 

In summary, the addition of a protected operator 
compartment to a model 506C-5 double bridge carrier 
requires both increased operator skills and significant 
machine modifications. The increased length and width 
caused by the addition of the compartment requires a 
higher skilled operator to handle the machine's reduced 
maneuverability. The modifications required to incorpo- 
rate the operator compartment to existing 506C-5 
machines are of such magnitude and cost that change is 
essentially precluded on a retrofit basis. However, the 
practicality emd costs for the compartment are reasonable, 
provided a modified machine is built with provisions for 
the compartment. 



PRELIMINARY DESIGN AND ANALYSIS 



Having established a basic location for the operator 
compartment, designers began to study concepts for 
compartment design and its attachment to the main 
frame. This effort included a review of previous programs, 
further investigation of required modifications to the basic 
machine, and compartment evaluation through the use of 
a full-scale mockup fabrication. 

The model 506C-5 bridge carrier is trammed at speeds 
and frequencies more like those of continuous miners than 
those of haulage vehicles like shuttle cars. Therefore, the 
operator compartment techniques employed on con- 
tinuous miners seemed most useful to this project. 

Previous studies had shown the advantages of a 
floating compartment (one which rides the floor) for use in 
low seams. Therefore, the floating-type design was chosen 
for the bridge carrier compartment. 

Single pivot point design compartments have been 
successfully used on Jeffrey mining machines, particular- 
ly a larger-height double bridge carrier. Preliminary 
design of the low-seam bridge carrier compartment placed 
its length at approximately 6 ft, requiring that the 



attachment design allow freedom for the compartment to 
pivot in the vertical plane with respect to the main frame. 
While this freedom could have been provided by freeplay 
in a floating entrapment, a pivot joint appeared more 
desirable. 

Consideration was given to providing for the compart- 
ment to rotate about a horizontal axis normal to the pivot 
axis. However, the width of the compartment did not 
appear to justify this added complexity. 

An attachment combining both the pivot and the 
sliding entrapment in the vertical plane is shown in figure 
11. The three views illustrate how the angle between the 
main frame and the compartment might change wi^h 
undulations in the floor. Note that the compartment side 
of the pivot brackets slide vertically within the entrap- 
ments on the compartment. 

Compartment attachment details were resolved and 
are described in a subsequent section. The basic design 
concept is pictured in figure 12. As shown, the entrap- 
ments are part of the two forward support posts of the 
canopy. 





FIGURE 11. — Attachment design employing a pivot and 
sliding entrapment. 



FIGURE 12. — View of compartment attachment used in final 
design. 



COMPARTMENT DESIGN 



The compartment design needed to provide the 
operator with adequate view of specific locations. Most of 
an operator's time is spent watching the receiving 
conveyor dolly position and responding to movements of 
the continuous miner. The operator must also watch the 
flow of material along the conveyors (including the two 
transfer points) and when tramming away from the face, 
the operator must have a clear view in the outby direction. 

Experiments with a long, narrow, and low compart- 
ment indicated the operator's desire for movement. 
Operator's frequently rolled their bodies to obtain a view 
in the outby direction. By making the compartment a 
keystone shape, more room can be provided to roll the 
torso over on an arm or elbow, thus allowing a rearward 
head turn while minimizing the compartment width at 
the attachment (or foot) end. The resulting compartment 
shape is shown in figure 12. 

In efforts to maintain a reasonable lengthening of the 
discharge conveyor, the compartment was designed to 
project forward approximately 2 ft into the area previous- 
ly occupied by components on the main frame. The crawler 
drive assembly was moved out an additional 1 ft from the 
conveyor. By moving the gear drive for the crawlers to the 
inby end, more clearance was provided for the compart- 
ment; this also helped to keep the center of gravity 
forward. 

Although only three canopy support posts were 
originally considered, a fourth post was added to 
maximize ease of operator ingress and/or egress, to 
improve operator protection, and to provide better support 
of the canopy. Mockup evaluation of the four-post 
structure showed no measurable degradation in operator 
ease of ingress or obscuration of visibility. 

The operator compartment seat was positioned approx- 
imately 19° away from parallel to the conveyor (figure 
13) for the followring reasons: the operator faces directly at 
the dolly position, the major task concern; easier ingress 
and/or egress; more space for controls and an armrest; and 
the operator can now see outby without having to make a 



180° head turn. At the widest point of this configuration, 
the compartment does not exceed the width of the outer 
edge of the crawler drive. 

The compartment floor was dished upward around the 
edges to prevent digging into the mine floor as the carrier 
moves. This is especially important in the area behind the 
operator; otherwise, significant material could be plowed 
loose during rearward motion, resulting in a buildup that 
would push the compartment upward. The goal of height 
selection of the dished sides was to minimize the 
accumulation of coal within the compartment. 

Figure 14 shows a side view of the double bridge 
carrier with the compartment in place. A solid or 
closed-top canopy was employed. In very low seams, the 
clearance between the canopy and roof is so small that 
there is no need for the operator to see the roof overhead. 
Therefore, a solid canopy does not obstruct operator 
visibility. 

The canopy was designed with adjustable height pin 
supports, adequate for most mine applications. This 
design is simpler and less expensive than hydraulically 
adjustable posts. Where mine conditions require frequent 
resetting of canopy height, hydraulic adjustment can be 
provided. Hydraulic lines routed to actuators behind the 
operator could be placed in the compartment floor lip area, 
adjacent to the conveyor. If necessary, a shield could 
protect these lines. 

Various split or semi-split canopies were evaluated 
(fig. 15). The reduced canopy area allowed a smaller 
height clearance between the canopy and the roof 
However, investigation showed that operator visibility 
was impaired in important directions by the canopy and 
the protective grid. 

A two-piece, split canopy would have to be over 5 ft 
long because it must extend from behind the heads of 
reclining operators to below their knees. The lower half of 
the canopy could only extend over the operator's feet and 
shins without being too high to obstruct line-of-sight to 
the receiving conveyor. Even if the top canopy were pairtly 



10 



ir-8"± 



3'-9" 



8' -8" 




FIGURE 13. — View of compartment shape. 



m 



^ ^^^^:^^ ^ 



i^ 



/t^VAVy/lVV^AV/'^ 



FIGURE 14. — Side view of bridge carrier with compartment in place. 




View through ribs at 20° 



FIGURE 15.— Compartment concept using split canopies. 



11 



open grid, it would be difficult to support almost 5 ft of 
overhang. Also, 5 ft versus 6 ft is not enough difference in 
the top area to justify that approach. 

SEAT AND CONTROLS 

Operator space within the compartment is approximate- 
ly 5V2 ft long by 30 in high at the lowest usable setting. 
These dimensions require a 60° from vertical back angle to 
accommodate a 95th percentile male. These were approx- 
imately the same dimensions used in the videotape 
studies. 

Given the above space dimensions and the static test 
results, the best choice for postural configuration was the 
reclining operator supported by a back recline angle of 60° 
from vertical. The seat design must include lumbar 
support and have an adjustable back tilt to permit smaller 
operators to sit in a more upright position. The seat pad 
length should be no greater than 17 in to avoid cutting off 
circulation in the legs of smaller operators. Footrests 
permit postural leg changes to deter stretching out the 
legs, which in time, stretches the hamstring muscles and 
puts pressure in the back of the thighs, producing blood 
circulation problems. 

A perforated fiberglass seat cushion that permits coal 
dust to filter through was selected as the best choice of 
fabric. An adjustable style back and seat tilt were also 
chosen. The most critical aspect of good seat design is a 
good head and neck support device. It should be adjustable 
in length and rotation to accommodate different sized 
operators and to hold the operator's head upright during 
machine operation. The head and neck supporter should 
also allow for head recline during rest periods. An 
elliptical design with eccentric operation might accom- 
plish this purpose. The side view of such a head support is 
sketched in figure 16. 

A seat similar to one used in another low-seam 
haulage vehicle was selected for the mockup evaluation. 
This seat has fore and back adjustments, adjustable back 
tilt, and swing-away adjustable armrests. The seat pad 
was 2-in thick and had a vinyl fabric cover. Head support 
was obtained from a preshaped neck pad which adjusted 
vertically with respect to the seat back. After some 
modifications, this seat design proved satisfactory for the 
new operator compartment. The subsequent design 
included a new head or neck support, a more durable 
mechanism for the back tilt, and a more rugged set of 
armrests. The armrest on the controls side could have 
been made adjustable instead of swing-away. 

Only four controls are frequently used by the bridge 
carrier operator; the two (left and right) tram controls and 
the two (receiving and discharge) conveyor elevation 
controls. With the operator compartment in the location 
shown, these controls are spring centered (off) as on the 
base 506C-5 bridge carrier. Ability to operate both tram 
controls in the same or opposite directions, with only one 
hand, was maintained. To reverse direction, operators 
must rotate their forearms and hands on the controls; 
therefore, the tram controls are located at the end of the 
armrest and move up and/or down in a near vertical plane 
with a backward tilt of approximately 15° to 20°. The 
bridge elevation controls are mounted adjacent to the 
tram controls and move up and down in the same plane of 
motion as the conveyors. Placement and handle styles 
provide the operator with tactile feedback as to which 
control is being operated. 



Bridge elevation controls are accessible to both hands. 
They are not used as frequently as the tram controls and 
the operator's left arm need not be supported during their 
operation. As noted during the underground mine visits, 
the operator often keeps both hands on the tram ocntrols 
for extended periods of time. Consequently, a good arm 
support was designed to facilitate this operating position. 
One concept for these controls is shown in figure 17. Some 
adjustability for the controls and armrest position were 
required. 

For easy access and to keep hydraulic hoses out of the 
operator compartment, the hydraulic valves were 
mounted on the machine main frame. Rods were used 
between the controls and the new operator levers. These 
rods were carried through the attachment that allows 
compartment up and/or down and pivot motion. Special 
provisions were made for the control rods to pass through 
the attachment point. 

Figure 18 shows the design concept for the control 
rods that transmit the operator's movement of the 
hydraulic controls. Although some small translation of 
the rods occurs as a function of the compartment's vertical 
position with respect to the machine main frame, the 
proper choice of dimensions in the detailed design keeps 




Set screw knob 
(not shown) 



Fixed mount 
-Tension spring 
Locking screw 

A Seat back 

VIEW A-A 

FIGURE 16. — Side view of liead support concept. 



Electrical control cable 




FIGURE 17.— View of concept for operator controls. 



12 



-Push-pull cable 

Cable clamp located 
on backside of plate 




Cable clamp bracket 
located on pipe 



Machine baseline 
and ground line 



Z 



Actual length of cable 

between these two 

points = 18 in 



6 "in ground 
clearance 



Compartment raised 6 in above ground line 
FIGURE 18. — Detailed view of control rods. 



this movement t6 an insignificant value. The rods slide 
through bushings on the compartment side of the pivot 
and the rods are pivoted on the main frame side of these 
bushings. 

Because the electrical controls are infrequently used, 
pushbutton controls were employed. These are the same 
type of controls used in the larger model Jeffrey 524 
double bridge carrier. The electrical controls are mounted 
as shown in figure 17. An emergency stop bar (not shown 
in the figure) is mechanically linked to these controls and 
can be easily activated by the operator's arm or leg. 

MOCKUP EVALUATION 

The mockup evaluation was performed in two steps. 
First, a simple wooden compartment was fabricated so 
that various operator positions within a compartment 
could be studied. One objective of the initial mockup was 
to establish overall compartment dimension require- 
ments. As mentioned in the operator position section, a 
variety of body positions were considered along with such 
factors as whether a seat should be provided, whether a 
simple movable bodyrest would be better, and whether the 
compartment should have hinged floor boards that can be 
raised at either end to serve as a tilted backrest. This 
compartment was used in conjunction with simple 
corrugated cardboard shapes simulating the mobile bridge 
carrier. 

After the evaluation established the importance of a 
reclining seat and determined the operator position to be 
most beneficial at an angle with respect to the conveyor, a 
new shape for the compartment was defined. A new 
wooden compartment shell with three pin-adjustable posts 
supporting the canopy was fabricated. Initial results from 
the cardboard shapes mockup were favorable, alleviating 
the need to make a complex machine wooden mockup. 
Additional portions of the machine were represented by 
vinyl fabric-covered cardboard shapes. The full mockup 
used in the detailed evaluation is shown in figure 19. 

The receiving conveyor dolly was represented by the 
shape on top of the conveyor in the center foreground of 
figure 19. This is the area watched most often by the 
operator. Figure 20 is the view toward the simulated dolly 
from the operator's eye location. The vertical scale seen 
beyond the dolly shows the distance above the floor. This 




FIGURE 19.— View of full-scale moclcup. 




FIGURE 20. — Operator's view toward simulated dolly. 



scale was repositioned for measurements during the 
visibility study. Note that only key shapes affecting 
visibility and/or compartment clearance were included in 
the mockup of the double bridge carrier. 

Figures 21 and 22 show how the operators can turn or 
roll their bodies to see outby. In these pictures, the 
operator is under a 36-in-high canopy setting with his 
right hand on the tram controls. Note that the final 
control orientation is shown in figure 17 rather than as 
shown here. 



13 




FIGURE 21.— View of operator looking outby. 




Figure 21 shows how an operator's left hand can reach 
across to operate the infrequently used conveyor elevation 
controls. The additional compartment width in the head 
and shoulders area is necessary to provide room for the 
torso to adequately twist and roll. Sturdy, properly placed 
armrests are important factors affecting operator comfort 
during these movements. 

The mockup served as the tool for conducting studies 
of the operator's visibility. The model 506C-5 operators 
have considerable freedom of motion to aid their sight in 
any direction, and if necessary, they can move essentially 
around the crawler drive assembly. 

Figure 23 is a plan view showing four reference points 
used in the evaluation; position 2 is the inby transfer point 
and dolly, and position 4 is the outby transfer point. 
Positions 1 and 3 are locations on opposite sides of the 
machine and are sometimes in the line-of-sight of the 
continuous mining machine operator. 

The visibility study was conducted using operators 
from the 5th, 50th, and 95th percentile male standards. 
The subjects were seated in the compartment with the 
seat back adjusted to its maximum angle. Evaluations 
were conducted at canopy height settings of 30, 32, 34, and 
36 in. Results of the study are given in table 3. 

Eye level values were calculated by first measuring 
the distance from the operator's eyes to the bottom surface 
of the canopy, then subtracting this value from the known 
distance from the floor to the canopy. For a given operator, 
eye level values and seat angle varied as a function of 
head tilt. As the operator's head laid back, the distance 



®. 



iJ 




KEY 



FIGURE 22. — Second view of operator looking outby. 



Q Reference points for visibility studies 
FIGURE 23. — Reference points used in visibility evaluation. 



Table 3. — Mockup evaluation results with different sized operators 



Canopy 

height, 

in 


Seat back 
angle from 
vertical, ° 


Eye 

level, . 
in 




Visibility at noted location 
(above floor), in 




Compartment length 
required, in 


No. 1 


No. 2 


No. 3 


No. 4 


Legs bent 


Straight 


OPERATOR SIZE, 5% 


30 
32 
34 
36 


65 
60 

55 
50 


22 
25 
27 
30 


17-48 
17-46 
17-48 
17-50 


25-47 
25-47 
25-49 
25-52 


35-42 
32-42 
28-45 
24-45 


26-49 
25-47 
25-40 
26-43 


63 
52 
48 
44 


Nap 
60 
58 
54 


OPERATOR SIZE, 50% 


30 
32 
34 
36 


65 
60 
55 
50 


25 
26 
27 
30 


18-42 
17-42 
17-43 
17-46 


25-42 
25-41 
25-43 
25-47 


33-41 
30-39 
26-41 
24-45 


26-43 
26-41 
26-38 
26-43 


72 
54 
56 
51 


Nap 
69 
69 
65 


OPERATOR SIZE, 95%' 


32 
34 
36 


60 
55 
50 


23 
25 
29 


17-47 
17-46 
17-48 


25-44 
25-44 
25-48 


32-42 
27-43 
25-46 


26-47 
26-47 
25-42 


58 
58 
58 


72 
72 

74 



'Operator unable to adapt to a 30-in canopy height at this operator size. 



14 



above the floor actually increased to a peak until 
continued movement caused a decrease. The degree of 
operator head tilt was determined by operator comfort and 
the severity of the angle at which the cap lamp was aimed 
forward. 

During the study, some suggested that the operators 
not wear the cap while under the canopy to increase their 
comfort. This suggestion was disregarded because cap 
light signals are a primary means of communication 
between the bridge carrier operator and other section 
workers. Cap lamp communication is especially important 
during times when the operator has both hands on the 
controls and wants to signal. 

Visibility data are given in table 3, which notes the 
lowest and highest visible readings on the various scales. 
As expected, operator field of view improved with 
increased canopy height. The operator had no apparent 
problem seeing the roof in the area above the dolly 
(position 2). 

The operator must judge the distance of the receiving 
conveyor above the floor by visually comparing the 
clearance between the dolly and the roof Additionally, the 
operator is not able to directly see spillage at the inby 
transfer point. Although overall visibility toward the 
dolly is good, the viewing angle is along the conveyor and 
some operators may find it difficult to judge the dolly 
position. If necessary, the problem can be eased by the 
addition of a position indicator. 

Rearward field of view is operator dependent as it 
relies on their agility in turning and rolling their bodies. 
The compartment caused no restriction to operator view in 
the outby direction. 

As part of the study, each operator configuration was 
photographed. (See figures 24 through 28.) As shown, the 
50th percentile operator was comfortable with the canopy 
set at 30 in, but the hard hat and lamp had to be tipped 
forward for the light to be useful. An adapting bracket 
might be added to the hat to help aim the lamp downward. 
Figure 25 is a view across the dolly toward a 5th 
percentile operator under a 32-in canopy. In all cases, the 
cap lamp and the operator's eyes were visible from this 
position. 



The 30-in canopy setting could not accommodate the 
95th percentile operator; figures 27 and 28 show the tight 
fit with the canopy set at 32 in. In figure 27, note the 
proximity of the operator's knees to the canopy, thus 
precluding further consideration of the previously dis- 
cussed split canopy. 

Figures 24 through 28 also show the compartment's 
openings for ingress and egress and the relative ease with 
which an operator could roll into or out of the compart- 
ment. If a rib or other obstruction blocked the normal 
route of egress, the operator could also exist by lowering 
the seat back. 

The mockup was evaluated for improving the follow- 
ing human factors: 

1. Side and rear protection for the operator should be 
increased. 

2. Footrest strips, 3- to 4-in high, should be provided 
across the floor of the compartment for postural relief. 

3. Provisions should be made for operators with 
bifocal glasses who would have difficulty operating with 
their heads laid back and their eyes sighted across their 
noses. (The need for better head and neck support was 
discussed earlier.) 

4. The seat's lumbar support should be increased 
between the pad and the back cushion during large back 
recline angles. Also, a seat pad tilt would be desirable. 

5. Operator activity should be increased to prevent 
potential operator alertness problems. 

6. Egress should be simplified or the operator might 
be less inclined to leave the compartment to perform other 
chores like cleanup or unclogging. 

In addition to the first three items above, several 
points were considered in the detail design phase; for 
example, seat selection. This decision involved choosing a 
seat design that still allowed clearance of the cap lamp 
battery and self rescuer. Other points included: avoiding 
sharp corners, providing handholds to facilitate ingress 
and/or egress, and movable or fixed controls (to compen- 
sate for seat-operator positions). 




FIGURE 24.— View of mockup compartment with 50th percentile operator under a 30-ln canopy. 



15 




FIGURE 25. — View across dolly toward a 5th percentile operator under a 32-in canopy. 




FIGURE 26.— View of mockup compartment with 50th percentile operator under a 36-ln canopy. 



16 





FIGURE 27. — View of mockup compartment with 95t>i percentile operator and 32-in canopy. 




FIGURE 28. — Second view of mockup compartment with 95th percentile operator and 32-in canopy. 



DETAILED DESIGN OF THE OPERATOR COMPARTMENT 



At this point, efforts were abandoned to develop a 
protected operator compartment, installable on a retrofit 
basis, for a model 506C-5 mobile bridge carrier. As 
previously detailed, the required pysical changes to the 
base machine to allow for installation of a protected 
operator compartment were of such magnitude, complex- 
ity, and cost that such an installation was essentially 
precluded. However, Jeffrey Mining Machinery was 
concurrently involved in the design of a new mobile bridge 
carrier with greater conveying capacity than the model 
506C-5. Jeffrey agreed to allow for inclusion of the newly 



developed operation compartment on its new machine, 
eventually marketed as the model 5010. 

Considerable effort went into the detailed design of 
the operator compartment and its attachment to the 
bridge carrier. The original concept was changed by 
moving the operator controls from the left to the right side 
of the machine. The idea was to keep the bridge carrier 
operator on the same side of the entry as the operator of 
the Jeffrey model 101 continuous miner; a unit commonly 
employed with the Jeffrey line of bridge carriers. (See 
figure 29.) 



17 




FIGURE 29. — View of compartment on right side of bridge carrier. 



The operator compartment was designed to attach to 
the mainframe through pivots and shdes. Figure 30 shows 
a close-up view of the attachment during mobility testing. 
Note that the compartment is inboard of the track (under 
the oil tank on the left) at the attachment points. To 
accommodate the compartment, the new bridge carrier 
was made 9-in longer and almost 4-ft wider than the 
model 506C-5 bridge carrier. The new bridge carrier 
design also required longer crawler tracks. 

The comp£trtment was attached to the mainframe by 
two pivots with horizontal axes. The compartment side of 
the pivots consists of steel collars that slide vertically 
along the two front canopy support posts. The slide travel 
was limited to 8 in by support members at the bottom and 
fixed collars at the top. Angular movement of the 
compartment with respect to the discharge conveyor was 
limited in the upward direction by a stop on the conveyor 
and in the downward direction by a link chain. 

The slides and pivots were tested at the manufactur- 
ing facility. The range of motions allowed by the 
attachment are (fig. 31) rear tilt upward, (fig. 32) slides up 
with rear tilt downwards, and (fig. 33) compartment level 
at the top of the slides. 

Selection of an operator seat for the compartment was 
limited by availability. In this case, the seat selected had a 
backrest separate from the seat unit. A new adjustable 
seat moimt was designed using data from the functional 
mockup evaluation. A single lever on the seat back 
retracts dual pins that engage in holes in the seat mount. 
This provides reclining vertical positions of 25°, 34°, 43°, 
51°, or 60°. A similar arremgement allows for adjustment 
of the seat cushion at horizontal angles of 10°, 20°, or 30°. 




FIGURE 30. — Close-up of compartment attachment hardware. 



18 




FIGURE 31. — View of compartment with rear tilted up. 




FIGURE 32. — View of compartment with slides up and rear tilted down. 




FIGURE 33. — View with compartment level and at top of slides. 



19 



The adjustment holes are shown in figure 34. A clevis pin 
through holes in the seat mount allows for nine fore-aft 
position selections in 1-in increments. 

Armrests that tilt back for ingress and/or egress were 
originally provided; however, the left armrest was 
removed because it interfered with arm movement and 
other compartment activities. 

During operation of a model 506C-5 bridge carrier, 
the operator kneels on the floor facing the machine and 
needs only a 90° head turn to see both inby and outby 
operations. (See figure 3.) 

Unfortunately, in the newly designed Jeffrey 5010 
machine, there was not enough room to place a compart- 
ment with the operator facing the machine as is the case 
in the model 506C-5. The new design compromised by 
placing the operator at a small angle (19°) with respect to 
the longitudinal axis of the machine. This angle helps 
operators considerably when turning their heads to see 
the outby transfer point. However, most operators sitting 
in the reclining position still must roll their bodies 
slightly off the seat to turn to see outby. 

Four posts Were required to support the canopy 
because of its large size and the weight of the loads it must 
support. The posts are telescopic and each is pin 
adjustable in 2y2-in increments for canopy heights from 30 
to 42V2 in. The adjustment increments used in the final 
design differed from the 2-in adjustment increments used 
in the mockup studies. 

During the compartment design phase, the Solar Fuel 
Co. (SFC) showed an interest in this program and agreed 
to an in-mine evaluation of the machine at its No. 9 mine. 
Because the seam height at this mine has considerable 
variation and undulations, SFC desired a method to 
change canopy height without using extra equipment 
such as jacks. Two hydraulic-lift cylinders were added to 
the compartment; one at the left rear (fig. 35) and the 
other at the opposite corner. 

A small pump with an oil reservoir and a reversing 
valve comprised the rest of the canopy raise system. The 




pump was operated by stroking the handle with flow 
direction set by the valve. The first step in adjusting the 
canopy height was to pump-up the circuit, lifting the 
weight of the canopy off the four pins for removal. The four 
adjustment pins must then be replaced in the desired 
height setting before the operator enters the compart- 
ment. Figure 36 shows, left to right; the hydraulic pump, 
the flow direction valve, the raise cylinder, and the 
support post. Both the electrical and hydraulic controls 
were located to the left of the operator so as not to impede 
ingress and/or egress. 




FIGURE 35. — View of canopy hydraulic lift cylinders. 




FIGURE 34. — View of seat adjustment fioles. 



FIGURE 36.— View of support post raise cylinder, flow- 
direction valve, and hydraulic pump. 



20 



EVALUATION PRIOR TO SHIPMENT 



Visibility measurements for the actual machine with 
compartment were repeated prior to shipment to the test 
mine. As previously noted, the compartment was located 
on the right, rather than the left, side of the bridge carrier. 
This was the only difference in the procedures used for the 
two tests. 

A camera was positioned in the operator eye location 
and pictures were recorded at each of the marker 
locations. With the canopy set at 30 in above the floor, 
operator field of view was very limited. As shown in figure 
37, operator field of view was limited to 43 to 47 in. When 
the canopy was raised to 35 in (fig. 38), operator field of 
view values improved to 23 to 56 in. At a canopy height of 
40 in (fig. 39), excellent values of 22 to 75 in were 
measured. 



When observing the bridge carrier outby transfer 
point, the operator's field of view angles are limited. 
However, this poses no real problem as the operator does 
not have to see over a large vertical angle; vision of only 
coal flowing across the transfer point is acceptable. 
Operator field of view for this situation was judged to be 
adequate for all canopy height and operator size combina- 
tions. 

Another consideration was visibility toward the 
general outby direction when the machine was tramming 
outby. In this situation, the operator usually turns in the 
opposite direction, as when observing the outby conveyor 
transfer. Although there was very little field of view 
obscuration in this direction, the operator (fig. 40) had to 
strain to see, even with a canopy setting of 35 in. 





RGURE 37.— View of visibility limits with canopy set at 30 In. 



FIGURE 38.— View of visibility limits with canopy set at 35 In. 





RGURE 39.— View of vtsiblltty limits with canopy tat at 40 In. 



FIGURE 40.— Vi«w of operator position to sss In gsnsrai 
outby dirsction. 



21 



The visibility was reasonable at most canopy heights 
except for 30 in. If operator size is not much over the 50th 
percentile and mine conditions are good, then operation 
with the canopy at 30 in is possible. Table 4 summarizes 
the visibility data collected using subjects in the machine 
before it was shipped to the mine. 



Canopy heights of 35 in or more are reasonable on 
this particular mobile bridge carrier as the viewing 
window is large enough for good visibility angles. A 
perspective on the window may be obtained from figure 
41, which is a photograph looking at the 5th percentile 
operator in the compartment with the canopy set at 35 in. 



Table 4. — Summary of collected visibility data 



Canopy 

height, 

in 


Seat back 
angle from 
vertical, ° 


Seat cushion 
angle from 
horizontal, ° 


Visibility^ at noted location 
(above floor), in 

No. 1 No. 2 No. 3 


No. 4 


Seat cushion to 

bottom edge of foot 

rest in distance, in 


OPERATOR SIZE, 5% 


30 
32.5 
35 
40 


43 
34 
34 
25 


30 
30 
30 
30 


NM 34-47 
NM 25-46 
NM NM 
NM NM 




NM 
NM 
NM 
NM 


NM 
NM 
NM 
NM 




15.5 
15.5 
18.5 
18.5 


OPERATOR SIZE, 50% 


30 
35 
40 


60 

51 
34 


30 
30 
30 


30-41 28-38 

NM 23-56 

24-56 22-75 




26-34 

NM 

24-75 


14-34 

NM 

16-56 




18.5 
21.5 
23.5 


OPERATOR SIZE, 95% 


30 
32.5 
35 
40 


60 
60 
51 
34 


20 
20 
20 
10 


NM 27-35 
NM 22-42 
NM 21-50 
NM 16-64 




NM 
NM 
NM 
NM 


NM 
NM 
NM 
NM 




18.5 
18.5 
19.5 
23.5 



NM No measurement. 

'Paired numbers indicate the height range, in inches above the mine floor, visible to the operator at each location. 




RGURE 41.— View Into operator compartment with canopy set at 35 In. 



22 



As shown in figure 42, the 5th percentile operator fits 
well within the confines of the compartment. In this case, 
the canopy was set at 35 in. This operator set the seat back 
angle at 34° from vertical and the seat bottom at 30° from 
horizontal. 

When a 50th percentile operator was under the 35-in 
canopy (fig. 43), his head position was farther back, 
though still within the canopy confines. This operator 
positioned the backrest at 51° from vertical and moved the 
seat back 3 in more than the smaller operator. As a result, 
the upper limit of visibility was somewhat reduced. 

The large operator found the compartment a tight fit 
(fig. 44). In this picture, the canopy height is at 35 in and 
the backrest angle is 51° from vertical. 



Each operator had a different preference for leg 
positions. The 5th percentile operator preferred placing 
both feet flat on the floor. This seemed normal since his 
legs, being smaller, were less apt to be in his line-of-sight. 
Also, his legs were too short to comfortably reach the 
slanted footrest when the seat fore-aft position was 
reasonable for reaching the controls. 

The 50th percentile operator preferred the slanted 
footrest (fig. 45). Two of the hydraulic actuator control 
cables (as shown) were too short, causing them to touch 
the operator's left foot. The design data were corrected to 
call for longer cables, which would be out of the way, as 
the other two hidden control cables. 





^m^^ y 



FIGURE 42. — View of 5th percentile operator with canopy set 
at 35 in. 



FIGURE 43. — View of 50th percentile operator with canopy set 
at 35 in. 




I 



]-f ^^. 





FIGURE 44. — View of 95th percentile operator with canopy set 
at 35 in. 



FIGURE 45.— View of leg position for 50th percentile operator. 



23 



The favorite position for the 95th percentile operator 
was with legs crossed and on the floor (fig. 46). In this 
photograph, the canopy height is 40 in and the backrest 
angle is 34° from vertical. Another view of this operator 
position is shown in figure 47. Note that this operator used 
the headrest to support his shoulders instead of his head. 

Control operation is primarily accomplished by using 
the left hand. As shown in figure 48, there are four levers 



located in a console on the floor of the compartment to the 
left of the operator. Through cables, the levers activate 
hydraulic controls located on the mainframe. The two 
upper levers are for the left and right tram. Pushing them 
forward moves the machine inby, while pushing them 
rearward reverses the tram. Figure 49 shows both upper 
levers being pulled simultaneously. 




^-««w»Miii^|i»3*"*k 




FIGURE 46.— View of leg position for 95th percentile operator. 



FIGURE 47. — View of 95th percentile operator with canopy set 
at 40 in. 





FICiuriE 48. — View of lever controls located in console. 



FIGURE 49.— View of operator activating both tram controls. 



24 



Two controls located on the console work the 
receiving and the discharge conveyor booms. When it is 
pushed upward, the left control raises the discharge 
conveyor, and lowers it when it is pushed down. The 
receiving conveyor works similarly with the right control 
lever. Figure 50 shows the operator's left hand (though not 
pictured) working the discharge conveyor raise-lower and 
the right hand working both tram controls. 

All electrical controls were located within the 
enclosure mounted high on the left wall of the operator 
compartment. This was an existing control box, which had 
already been approved by MSHA for use on another 
machine. Figure 51 shows the details of the electrical 
controls. The fire extingusiher is located below the 
electrical control case, and the actuator knob is visible just 
above the backrest in figure 51. 



Figure 52 shows the typical reach to start the pump 
motors. Although the electrical control buttons may be 
actuated with the left hand, it is more natural to use the 
right hand. The far left control is the hardest to reach (fig. 
53). This is seldom used and will shut down the continuous 
mining machine as well as the haulage system. Note that 
the panic bar may be operated either with the left 
shoulder or a hand. 

If desired, the operator can work both the electrical 
£md hydraulic controls at the same time (fig. 54). Note that 
this view is with the 50th percentile operator and canopy 
setting of 30 in. 

Figure 55 shows the large operator working the 
hydraulic controls while looking back in the outby 
direction. The canopy in this picture is set at 35 in. 





FIGURE 50.— View of operator working discharge con- 
veyor raise-lower and tram controls. 



FIGURE 51.— Detailed view of electrical controls. 





FIGURE 52.— View of operator reach required to start pump 
motors. 



FIGURE 53.— View of operator reach required to use 
leftmost pump control. 



25 





FIGURE 54. — View of operator working both electrical and 
hydraulic controls. 



FIGURE 55. — View of 95th percentile operator working 
hydraulic controls while looking outby. 



UNDERGROUND EVALUATION 



An in-mine evaluation was conducted through the 
cooperation of the SFC at its No. 9 mine, located near 
Somerset, PA. Seam height at this mine generally varied 
from 40 to 46 in, but frequently pinched down much lower. 
Entries and crosscuts were 20-ft wide. Overall moisture, 
roof, and floor conditions were fair. 

The new bridge carrier (Jeffrey model 5010) with 
operator compartment was substituted on an operating 
section for a Jeffrey model 506C-5 bridge carrier. Machine 
installation occurred in October 1981, with a 3-month 
evaluation planned. The evaluation period was extended 
to 10 months for a variety of reasons that included 
interruptions to the mining operation, unrelated to the 
new bridge carrier. The bridge carrier with operator 
compartment was removed from the mine in October 
1982, and was delivered to the Bureau's facilities at 
Bruceton, PA. 

The new bridge carrier was trammed into the mine 
from the highwall entrance. In order to clear the roof, the 
canopy height was set at 30 in. Coal, mud, and water filled 
the compartment floor because of several low areas with 
accumulated water. The edges of the compartment were 
angled around the periphery in order to make the 
compartment ride over, rather than dig into, the floor 
during tramming (fig. 56). This feature also caused the 
floor to retain water when the drain holes became blocked. 
The water accumulation was cleaned out when the 
machine was installed on the section; subsequently, 
reoccurrence of buildup required only infrequent cleaning. 

At the working section, the mine operator tried the 
35-in canopy setting, but settled on the 37.5-in and 40-in 
settings soon thereafter. Some places in the section had 
little clearance between the canopy and the roof with the 
canopy set at 40 in (fig. 57). During the in-mine operation, 
the compartment floated well along the floor because of 



the slides and pivots. As a result, the canopy to roof 
clearance measured as much as 6 in at certain locations. 

Operator field of view was fairly good with the canopy 
set at 40 in. Figure 58 is a view looking back toward the 
compartment. 

The mine added a protective metal mesh, angled 
inward, onto the top of the compartment wall before 
bringing the machine into the section. The mesh was 
intended to curtail the possibility of the operator being 
pinched by relative movements between the compartment 
and the discharge conveyor. The mesh did not significant- 
ly block the operator's view toward the opposite side of the 
machine. 

The discharge conveyor may be raised several inches 
from the horizontal position. Figure 59 is a view from the 
left front of the machine with the conveyor raised close to 
the roof. While the conveyor obscures 'Vision directly 
across the machine, it does not otherwise affect operation. 
The conveyor is lower when tramming the machine, which 
allows the operator to see through the mesh and across the 
machine. 

Four different operators of the double bridge carrier 
were observed during the in-mine evaluation: one 50th 
percentile male, two 40th percentile males and one 60th 
percentile female. Figure 60 shows that a 50th percentile 
operator fits well within the compartment with a canopy 
height of 40 in. This view was taken while running coal. 
Note the operator's right hand is resting on his right leg 
with no support from the back armrest. This posture was a 
matter of individual preference because the operator 
believed that he was comfortable enough without having 
to move the armrest for egress and/or ingress. Also, note 
that the operator's knees are raised with both feet still on 
the slanted footrest. 



26 



Figure 61 is a close-up of a smaller operator with his 
left hand on the tram controls and the canopy set at 37^2 
in. He preferred to use the armrest and placed his hand on 
his lap. 

Operator indoctrination occurred quickly once the 
operator got over the restless reaction resulting from 
confinement within the compartment. Inability to directly 
see the inby conveyor carriage posed the greatest problem. 
Using the new machine, movement between stops is 
limited to only 5 ft, which means the operator must be 
skillful in moving the bridge carrier to avoid banging the 
carriage against the stops as a result of continuous miner 
movement. When seated in the compartment, the operator 
can see only the top of this carriage. 

Each operator preferred different working positions 
within the compartment, with frequent repositioning to 
retain reasonable comfort. Because the operators had 
little to do within the compartment, they tended to become 
inattentive. In efforts to alleviate boredom, operators were 
encouraged to get out of the compartment frequently to do 
spillage cleanup and machine inspection. 



The operators were skillful in tramming the bridge 
carrier inby and outby. When the panline was on the left 
side, the operators attempted to maintain 3 ft of clearance 
between the compartment and the right rib. When the 
panline was on the right side, it was easier to see. 

After 1 to 2 months of operating the machine, two 
operators complained of backache. It was not determin- 
able whether these complaints really resulted from 
operating the double bridge carrier or were injuries from 
some unrelated cause. Later operators of the machine 
never expressed any backache complaints. If the backache 
complaints are justified, a better seat should be designed 
that would still be economically acceptable. 

Difficult mining conditions, due to incursions of stone 
into the coal seam, precluded a good measure of the effect 
that adding an operator compartment onto the double 
bridge carrier would have on coal production. From the 
data collected, it appeared that the production rate 
remained unchanged from that of the section when using 
the model 506C-5 bridge carrier. 





FIGURE 56. — View of rear of operator compartment showing FIGURE 57. — View of roof clearance with canopy set at 40 

dished sides. in. 




JEFFREY A'BOlrt 



FIGURE 58. — View into the operator compartment. 



FIGURE 59.— View of conveyo: when raised close to roof. 



27 





FIGURE 60. — View of operator working within compartment. 



FIGURE 61 . — View of second operator working within compart- 
ment. 



SUMMARY 



The project objective to develop a protective operator 
compartment for a low-seam mobile bridge carrier was 
achieved. Significant benefits of the project to the coal 
mining industry include: the compartment is available as 
a standard order item from a major equipment manufac- 
turer and is successfully being employed in several 
thin-seam mines; and workable, protective operator 
compartments can be achieved in working seams less than 
the present 42-in Federal requirement. 



Significant findings of the project include: 

1. A protective operator compartment for a thin-seam 
mobile bridge carrier was found feasible for use in coal 
seams as low as 40 in. 

2. The addition of the operator compartment did not 
appear to have any adverse effects on production rates. 

3. The general design philosophy of the bridge carrier 
compartment should be useful in designing protected 
operator compartments for other types of thin-seam 
mining equipment. 



8487 177 



ft U.S. GOVERNMENT PRINTING OFFICE: 1986—605.017/40,074 



INT.-BU.OF MINES, PGH., PA. 28369 



U.S. Department of the Interior 
Bureau of Mines— Prod, and Oistr. 
Cochrsns Mill Road 
P.O. Box 18070 
Pittsburgh. Pa. 15236 



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